Kuala Lumpur: Investigators probing the baffling disappearance of a Malaysian plane with 239 people aboard on Tuesday identified a 19-year-old Iranian man as one of the two persons who travelled on stolen passports but said he is "not likely" to have terrorist links.

"We have identified (one of the two persons travelling on stolen passports as) an Iranian by the name of Pouria Nour Mohammad Mehrdad. He is 19-years-old and he is an Iranian, we believe that he is an Iranian," Inspector General of Police Khalid Abu Bakar said in Kuala Lumpur.

"We have been checking his background. We have also checked him with other police organization on his profile and we believe that he is not likely to be a member of any terrorist group. We believe that he was trying to migrate to Germany," he was quoted as saying by BBC.

Authorities were in contact with the Iranian's mother in Germany, who has been expecting her son to arrive in the city of Frankfurt, he said.

The investigation into the fate of Malaysia Airlines flight MH370 widened with authorities questioning travel agents about the two men who boarded the plane with stolen passports of an Italian and an Austrian.

The Beijing-bound Boeing 777-200 plane had 227 passengers on board, including five Indians and one Indian-origin Canadian, and 12 crew members.

The police chief said that they had not finalized their probe on the other passenger who used a stolen passport.

"On the other person who travelled on the stolen passport, we are still conducting our investigation," he said.

Another Iranian man named Kazem Ali bought one-way tickets for the two men, describing them as friends who wanted to return home to Europe, a channel reported citing Thai police.

While Ali made the initial booking by telephone, either he or someone acting on his behalf paid for the tickets in cash, police said.

"We have to look further into this Ali's identity because it's almost a tradition to use an alias when doing business around here," Police Lt Colonel Ratchthapong Tia-sood said.

The travel agency's owner, Benjaporn Krutnait, said she believed Ali was not connected to terrorism because he had asked for cheapest tickets to Europe and did not specify the Kuala Lumpur to Beijing flight.

The search for the missing plane entered the fourth day, as 34 planes, 40 ships and teams from ten countries were involved in search operations that were widened to a 100 nautical mile (185 km) radius from the point the plane was last detected.

The Malaysian police chief contradicted aviation chief's statement yesterday that five people did not board the plane.

"There is no such thing as five person who did not board the plane. There is no such thing," Khalid said.

He said that the director of the criminal investigation department has been appointed to head the investigation into what happened and that they were looking at four different scenarios.

"We are looking into four areas: one; hijacking, two; sabotage, three; psychological problems of the passengers and crew and four; personal problems among the passengers and crew," he said.

"We are going through all the passenger manifests and our counterparts in at least 14 countries...and also from other parts of the world," he added.

The Malaysia Airlines, in a statement on Tuesday, said "The search and rescue teams (SAR) have expanded the scope beyond the flight path to the West Peninsular of Malaysia at the Straits of Malacca. The authorities are looking at a possibility of an attempt made by MH370 to turn back to Subang. All angles are being looked at. We are not ruling out any possibilities."

Vietnam's deputy military chief said he has ordered a land search for the plane up to border with Laos and Cambodia.

Azharuddin said a hijacking attempt could not be ruled out as investigators explore all theories.

A senior police official said that people armed with explosives and carrying false identity papers had tried to fly out of Kuala Lumpur in the past, and that current investigations were focused on two passengers who were on the missing plane with stolen passports.

"We have stopped men with false or stolen passports and carrying explosives, who have tried to get past KLIA (airport) security and get on to a plane," he said. "There have been two or three incidents, but I will not divulge the details," he added.

Azharuddin also said the two men with stolen passports did not look like Asians, but he did not elaborate. Airport CCTV footage showed they completed all security procedures, he said.

"We are looking at the possibility of a stolen passport syndicate," he said.

About two-thirds of the 227 passengers and 12 crew now presumed to have died aboard the plane were Chinese. The airline said other nationalities included 38 Malaysians, seven Indonesians, six Australians, five Indians, four French and three Americans.

A senior source involved in preliminary investigations in Malaysia said the failure to find any debris indicated the plane may have broken up mid-flight, which could disperse wreckage over a very wide area.

"The fact that we are unable to find any debris so far appears to indicate that the aircraft is likely to have disintegrated at around 35,000 feet," said the source.

Asked about the possibility of an explosion, the source said there was no evidence of foul play and that the aircraft could have broken up due to mechanical causes.

Still, the source said the closest parallels were the bomb explosions on board an Air India jetliner in 1985 when it was over the Atlantic Ocean and a Pan Am aircraft over the Scottish town of Lockerbie in 1988. Both planes were cruising at around 31,000 feet at the time.

Underlining the lack of hard information about the Malaysian plane's fate, a US Navy P-3 aircraft capable of covering 1,500 square miles (3,900 square km) every hour was sweeping the northern part of the Strait of Malacca, on the other side of the Malaysian peninsula from where the last contact with MH370 was made.

No distress signal was sent from the lost plane, which experts said suggested a sudden catastrophic failure or explosion, but Malaysia's air force chief said radar tracking showed it may have turned back from its scheduled route before it disappeared.

Superior safety record

The Boeing 777 has one of the best safety records of any commercial aircraft in service. Its only previous fatal crash came on July 6 last year when Asiana Airlines Flight 214 struck a seawall on landing in San Francisco, killing three people.

US planemaker Boeing declined to comment.

The passenger manifest issued by the airline included the names of two Europeans who were not on the plane. Their passports had been stolen in Thailand during the past two years.

An Interpol spokeswoman said a check of all documents used to board the plane had revealed more "suspect passports", which were being investigated.

"Whilst it is too soon to speculate about any connection between these stolen passports and the missing plane, it is clearly of great concern that any passenger was able to board an international flight using a stolen passport listed in Interpol's databases," Interpol Secretary General Ronald Noble said.

A Thai travel agent who arranged the tickets for the two passengers using the stolen passports said she had booked them on the flight via Beijing because they were the cheapest tickets, the Financial Times reported.

The travel agent in the resort of Pattaya said an Iranian business contact she knew only as "Mr Ali" had asked her to book tickets for the two men on March 1.

She had initially booked them on other airlines but those reservations expired and on March 6, Mr Ali had asked her to book them again. She told the newspaper she did not think Mr Ali, who paid her in cash and booked tickets with her regularly, was linked to terrorism.